Case in point would be the HP-41 Machine Design application pac. The HP sale flyers list it as HP 00041-15020, and this would be for the English language pac. This number is marked on the box of the English language pac.

I have two ROM's, both made in Singapore. Date code 2035 has the ROM marked HP 00041-15020. Date code 2303 has the ROM marked HP 00041-14010. Both catalog on the HP-41CX as "MACHINE 1A".